Moving lots of tasks to subtask ...

Can't figure this out ...
let's say I have 30 (or 100) tasks. I want to drag them all to be child/sub tasks of a parent task.
how do I do this without dragging each one?

and ...
while I am at it - since I tried doing a custom search/batch edit (thought I could)
I isolated the 30 tasks I want to be child tasks
but there was no way for me, via batch edit to move these under a specific parent task.

It would be nice to have kind of 'Selection mode' after choosing the proper option in the upper right menu, where we could select as many tasks we want from currently displayed list and perform various operations like changing Folders, Tasks etc., including draging into parrent task or deleting.

The only way I have ever found to do this is through a 3rd party app called "Ultimate To-do List". Not a very elegant answer to your question. I totally agree there should be a method to independently choose records and move them accordingly.

What I do to get around that lack of functionality is to make Parent Tasks in a single folder called "Today", "This Week", "Soon" and then I can drag child tasks from one parent task to another. I hate clicking on multiple drop down fields to do anything.